Amazon wants in on the digital advertising (and they have LOTS of shopping/product-searching data to mine), and Google is partnering with Wal-Mart and Target for e-commerce.
Google doesn’t have just search data, they have whole browsing history, geographic movements (Maps), your emails, offline purchases with Android Pay, etc. Amazon knows what you bought on Amazon, but Google knows what you bought basically everywhere.
Abrupt drop in activity hints at Amazon’s own ad ambitions
Two tech giants are increasingly competing on multiple fronts
Amazon.com Inc. has stopped buying a popular type of Google ad, according to people familiar with the decision. The move deepens the rift between the technology titans and signals Amazon’s growing ambition in the digital advertising market.
The pullback affects highly coveted real estate at the top of Google search results, where retailers and e-commerce bid and pay handsomely to place colorful, image-rich ads that show up when consumers look online for running shoes, headphones and other products to buy.